Python dictionary ' ' key error

Question

error showed I am running into a key error while trying to loop through a dictionary. If someone could tell me what I am doing incorrect, it would be helpful. I am trying to make a basic "Caesar cipher", a way to decode messages with an offset of 13. :)

ceasar = {'a':'n', 'b':'o', 'c':'p', 'd':'q', 'e':'r', 'f':'s', 'g':'t', 'h':'u', 'i':'v', 'j':'w', 'k':'x', 'l':'y', 'm':'z', 'n':'a', 'o':'b', 'p':'c', 'q':'d', 'r':'e', 's':'f', 't':'g', 'u':'h', 'v':'i', 'w':'j', 'x':'k', 'y':'l', 'z':'m'}
def ceasar_cipher(encoded):
    encoded = encoded.lower()
    decoded = ""
    for letter in encoded:
        if letter == "?" or letter == "!":
            decoded += letter
    for letter in encoded:
        ceasar[letter] += decoded
        print decoded

What are you calling the function with? I'm assuming there is a space in the words being passed and there is no `' '` in your lookup dict `caesar` - hence the key error. — AChampion, Mar 23 '16 at 16:49
Try changing your first assignment to `encoded = encoded.lower().strip()` — Bahrom, Mar 23 '16 at 16:49
fyi, Python includes a [caeser cypher with a key of 13](https://docs.python.org/2/library/codecs.html#python-specific-encodings): `import codecs; print(codecs.encode(message, 'rot_13'))` — RoadieRich, Mar 23 '16 at 17:02

score 0 · Answer 1 · edited Mar 23 '16 at 16:57

0

Here's another approach, can you give us some sample input and output? What do you want to do with characters that aren't in your caesar dict:

caesar = {'a':'n', 'b':'o', 'c':'p', 'd':'q', 'e':'r', 'f':'s', 'g':'t', 'h':'u', 'i':'v', 'j':'w', 'k':'x', 'l':'y', 'm':'z', 'n':'a', 'o':'b', 'p':'c', 'q':'d', 'r':'e', 's':'f', 't':'g', 'u':'h', 'v':'i', 'w':'j', 'x':'k', 'y':'l', 'z':'m'}

def caesar_cipher(encoded):
    print("".join(caesar.get(letter, letter) for letter in encoded.lower()))

edited Mar 23 '16 at 16:57

AChampion

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answered Mar 23 '16 at 16:52

Bahrom

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`caesar.get(letter, letter)` makes the `if letter in ...` unnecessary. – AChampion Mar 23 '16 at 16:54
Good point @AChampion thanks! I had added that edit later and forgot to take out the first check. – Bahrom Mar 23 '16 at 16:54
1

fixed a paren issue, and added `.lower()` – AChampion Mar 23 '16 at 16:57

score 0 · Answer 2 · answered Mar 23 '16 at 17:13

I think you want

ceasar = {'a':'n', 'b':'o', 'c':'p', 'd':'q', 'e':'r', 'f':'s', 'g':'t', 'h':'u', 'i':'v', 'j':'w', 'k':'x', 'l':'y', 'm':'z', 'n':'a', 'o':'b', 'p':'c', 'q':'d', 'r':'e', 's':'f', 't':'g', 'u':'h', 'v':'i', 'w':'j', 'x':'k', 'y':'l', 'z':'m'}
def ceasar_cipher(encoded):
    encoded = encoded.lower()
    decoded = ""
    for letter in encoded:
        if letter in ceasar.keys():
            decoded += ceasar[letter]
        else:
            decoded += letter
    print decoded

This preserves spaces, punctuation, and any other characters that are not in the translation dict.

Python dictionary ' ' key error

2 Answers2